Due to advances in device scaling for semiconductors, semiconductor device features have become smaller at the same time their aspect ratios have become larger. Consequently, semiconductor-device structures have become susceptible to damage from wet cleaning and drying. This susceptibility is exacerbated by the use of new materials in the process flows for semiconductor manufacturing.
In response to this susceptibility and other shortcomings in the technology for wet cleaning and drying, a system has been developed that uses mechanical and chemical cleaning to selectively remove residue without damage to semiconductor-device structures. This system transports a single semiconductor wafer linearly between an opposing pair of proximity heads that deliver a cleaning fluid to the wafer in an exposure time on the order of a few seconds.
In particular implementations, the cleaning fluid delivered by the opposing proximity heads is a high viscosity, non-Newtonian fluid in the form of a foam generated by mechanically mixing (a) a gas such as nitrogen (N2) and (b) a fluid containing water and a surfactant. See e.g., U.S. Published Patent Application No. 2006/0128600 entitled “Cleaning Compound and Method and System for Using the Cleaning Compound,” filed on Feb. 3, 2006, U.S. application Ser. No. 11/820,590 entitled “System, Method and Apparatus for Maintaining Separation of Liquids in a Controlled Meniscus” filed on Jun. 19, 2007, and U.S. application Ser. No. 12/185,780 entitled “Generator for Foam to Clean Substrate,” filed on Aug. 4, 2008. The disclosures of all three of these applications are hereby incorporated by reference.
If the surfactant is allowed to escape into the system's chamber during the deposition of the foam onto the semiconductor wafer, the surfactant can dry into a solid and contaminate later semiconductor wafers processed by the system. Consequently, a need exists for an inexpensive and effective means of confining the cleaning foam during its deposition onto a semiconductor wafer by the system. However, the invention claimed below has wide applicability to other applications beyond this particular application, as will become apparent from the following description and drawings.